1. Field of the Invention
The present invention relates to power supplies, and more particularly, to a variable switching frequency type power supply that can achieve high efficiency by fixing a switching duty cycle to 50% and varying switching frequency.
2. Description of the Related Art
In general, power supplies convert input power, supplied from the outside, into power having a current level or a voltage having a magnitude determined by a user, and supply the converted input power to corresponding apparatuses. The power supplies are widely used for home appliances and information communication devices, such as portable terminals, notebook computers, LCD monitors, and network servers.
The power supply alternately switches the input power at a switching duty cycle to convert the input power to usable power. Here, the switching duty cycle is generally set within a range of approximately 0.3 to 0.35 in order to ensure an operating margin for a voltage sag or a variation of input power.
Here, a circulating current interval occurs in which input energy is not transmitted to an output terminal but circulates within an input circuit. Therefore, zero voltage switching is not ensured. As a result, conduction loss is caused during switching, elements involved in the switching generate high heat, the efficiency of the power supply is reduced, and an increase in output ripple current occurs.